Field of the Invention
The present invention relates to a power semiconductor device with a switchable power semiconductor chip mounted on a lead frame.
Description of the Background Art
A power semiconductor device is configured by mounting a switchable power semiconductor chip on a mount surface of a lead frame shaped in a wiring pattern and sealing them with a mold resin. The power semiconductor device is used as a single unit or a plurality of units in combination in a power conversion circuit that is incorporated into various products including transportation equipment and home electrical appliances.
When energized, the power semiconductor chip generates heat so that a temperature increases. Then, a current flowing in the power semiconductor chip needs to be controlled so that the temperature will not exceed a predetermined allowable temperature. Specifically, suppressing transient temperature increase of the power semiconductor chip when energized allows current flowing in the power semiconductor chip to be increased, which improves the performance of the power conversion circuit.
For in-car equipment, the performance of the power conversion circuit affects the amount of torque for driving a motor or power generated by a motor. In such equipment, a large amount of current that reaches several hundred amperes in a short time may flow. Then, suppressing transient temperature increase of the power semiconductor chip when a large amount of current flows therein is one of the most important factors for causing the product to operate.
As one structure for suppressing temperature increase of the power semiconductor chip, for example, PTL 1 presents a semiconductor power module in which a metallized surface of a semiconductor chip is soldered to a heat diffusion plate. In this example, a heat diffusion plate formed of a sintered compact containing copper and a copper plate is used to improve the heat dissipation capability of the semiconductor power module at a cost lower than that at which a high heat-conductivity ceramic substrate is used.
[PTL 1] Japanese Patent No. 4,030,930
However, in the structure presented in PTL 1 in which the heat diffusion plate is provided under the semiconductor chip, a variation in the thickness of the solder junction on the top and bottom sides of the heat diffusion plate causes a variation in the height of the semiconductor chip, increasing the variation in thermal resistance. In order to prevent trouble or failure in use, product design needs to be based on the thermal resistance at a place in which variation in height is highest, which poses a problem of limiting the performance of the product.
Furthermore, providing the heat diffusion plate poses a problem of increasing the material cost and the module size. Furthermore, the solder junction on the top and bottom sides of the heat diffusion plate serves as a passage through which current flows. Then, variation in the shape of the solder junction needs to be suppressed, which causes a problem of decreasing the productivity.